A hub of the kind described above is disclosed in U.S. Pat. No. 4,088,212 and the corresponding French published patent application No. FR-2 363 731 A, in which the hub with its projections is obtained by pressing from sheet metal. The projections are disposed at the inner periphery of the hub plate, for the purpose of centring components of the torsion damper. The major disadvantage of this arrangement resides in the fact that the hub plate has a thickness the value of which is least in the region of the projections, and the fibres of the metal are broken up at this point. For this reason, the mechanical strength of the component is not as great as is desirable.
In addition, it is not possible to form protuberances in every location where they might be required, since their shape is influenced by the presssing operation and is dependent on the thickness of the hub plate.
In general terms, it is desirable to improve the mechanical integrity of the hub plate. One proposal for achieving this is disclosed in United Kingdom patent specification No. 812001, and comprises thickening the inner periphery of the hub plate to the detriment of the axial space available between the hub plate and the guide rings of the torsion damper.
Another proposal, described in U.S. Pat. No. 4,190,142, consists in splitting the monobloc hub into two, which inevitably leads to an increase in the radial bulk of the torsion damper.